build your own bridge readme

README.md

@@ -56,17 +56,54 @@ fetch the latest root of the World ID merkle tree using the
 [`WorldIDIdentityManagerImplV1`](https://github.com/worldcoin/world-id-contracts/blob/main/src/WorldIDIdentityManagerImplV1.sol)
 method named
 [`latestRoot()`](https://github.com/worldcoin/world-id-contracts/blob/42c26ecbd82fba56983addee6485d5b617960a2a/src/WorldIDIdentityManagerImplV1.sol#L433-L438)
-and then will use the native L1<>L2 bridge to send a message to the target L2 contract (e.g. `OpWorldID`). The messaging
-layer of the L2 will forward the message to the target contract and call it with the correct payload.
+and then will use the native L1<>L2 messaging layer to send a message to the target L2 contract (e.g. `OpWorldID`). The
+messaging layer of the L2 will forward the message to the target contract by calling the corresponding method on the L2
+contract with the specified payload from the L1.
 
 > [!NOTE] The current implementation of WorldID will only work for EVM-compatible networks as mentioned in the
 > [Supported networks](#supported-networks) and [Future integrations](#future-integrations) sections. If you are an
 > EVM-compatible rollup you also need to support the pairing cryptography and keccak256 precompiles.
 
+The root of the World ID Identity Manager tree is the only public state that you need to send to the L2 in order to
+verify Semaphore proofs (proofs of inclusion in the World ID merkle tree). As long as you have the root and a World ID
+implementation on your network, you can deploy World ID on it.
+
+#### Requirements
+
+- service to sync the World ID merkle tree (currently only done by
+  [`signup-sequencer`](https://github.com/worldcoin/signup-sequencer))
+- EVM support on the L2 (pairing cryptography and keccak256 precompile support needed)
+  - or a custom implementation of World ID for your execution environment (see
+    [Future integrations](#future-integrations))
+- native L1<>L2 data messaging layer (e.g. Optimism cross domain messenger, Arbitrum, etc)
+- relayer service that periodically calls `propagateRoot()` as a cron job (e.g.
+  [`state-bridge-relay`](https://github.com/worldcoin/state-bridge-relay))
+- deployment scripts
+- audits (World ID contracts, both `world-id-contracts` and `world-id-state-bridge` are audited by Nethermind
+  ([1](https://github.com/NethermindEth/PublicAuditReports/blob/main/NM0131-FINAL_WORLDCOIN_STATE_BRIDGE_CONTRACTS_UPGRADE.pdf),
+  [2](https://github.com/NethermindEth/PublicAuditReports/blob/main/NM0122-FINAL_WORLDCOIN.pdf)))
+
 #### Specification
 
 If you want to build your own state bridge, you can use the `OpStateBridge` contract as a template. The contract has two
-main methods, namely `propagateRoot()` and `setRootHistoryExpiry()` which you will need to implement
+main methods, namely
+[`propagateRoot()`](https://github.com/worldcoin/world-id-state-bridge/blob/main/src/OpStateBridge.sol#L126) (fetches
+the latest root from the
+[Orb/Phone World ID IdentityManager contract](https://docs.worldcoin.org/reference/address-book) and propagates it to
+the target L2 contract using the native L1->L2 messaging layer) and
+[`setRootHistoryExpiry()`](https://github.com/worldcoin/world-id-state-bridge/blob/main/src/OpStateBridge.sol#L170)
+(sets how long you want a propagated root to be valid for inclusion proofs) which you will need to implement. Most
+native bridges will have a messenger/relayer contract and a generic interface you can use to call a function on a target
+contract on the L2 with your desired calldata (which is the message). Another requirement for this system to work is to
+only allow the contract on L1 to be able to call this function on the L2, otherwise anyone would be able to insert
+arbitrary merkle tree roots into the L2 contract. On the `OpWorldID` contract we used a contract named
+[`CrossDomainOwnable3`](https://github.com/ethereum-optimism/optimism/blob/develop/packages/contracts-bedrock/src/L2/CrossDomainOwnable3.sol)
+which implements this functionality (checks that L1 sender is a given sender).
+
+> [!NOTE] If you want to support World ID on an OP-stack network it is very easy as we have already implemented it for
+> Optimism, the only change you need to make is within the deploy scripts where you need to set the
+> [crossDomainMessengerAddress](https://github.com/worldcoin/world-id-state-bridge/blob/main/src/script/deploy/op-stack/optimism/DeployOptimismStateBridgeGoerli.s.sol#L32)
+> to the your own network's cross domain messenger address on Ethereum L1 (whether mainnet or testnet).
 
 ## Documentation